1. Field of the Invention
The present invention relates to a method for forming a near-field light generating element that generates near-field light by receiving light. Further, the present invention relates to a thermally-assisted magnetic recording head provided with the near-field light generating element, for writing data by thermally-assisted magnetic recording technique.
2. Description of the Related Art
As the recording density of a magnetic recording apparatus, such as a magnetic disk apparatus, becomes higher, further improvement has been required in the performance of a thin-film magnetic head and a magnetic recording medium. As the thin-film magnetic head, a composite-type thin-film magnetic head is widely used, which has a stacked structure of a magnetoresistive (MR) element for reading data and an electromagnetic transducer for writing data.
Whereas, the magnetic recording medium is generally a kind of discontinuous body of magnetic microparticles gathered together. Here, one record bit consists of a plurality of the magnetic microparticles. Therefore, in order to improve the recording density, it is necessary to decrease the size of the magnetic microparticles and reduce irregularity in the boundary of the record bit. However, the decrease in size of the magnetic microparticles raises a problem whether the recorded information is stably held for a long time or not under fear of the degradation of thermal stability of magnetization due to decrease in volume.
As a measure against the thermal stability problem, it may be possible to increase the magnetic anisotropy energy KU of the magnetic microparticles. However, the increase in energy KU causes the increase in anisotropic magnetic field (coercive force) of the magnetic recording medium. Whereas, write field intensity of the thin-film magnetic head is limited by the amount of saturation magnetic flux density of the soft-magnetic pole material of which the magnetic core of the head is formed. Therefore, the head cannot write data to the magnetic recording medium when the anisotropic magnetic field (coercive force) of the medium exceeds the write field limit.
Recently, as a method for solving this problem of thermal stability, so-called a thermally-assisted magnetic recording technique is proposed, in which writing is performed by reducing the anisotropic magnetic field with heat supplied to the magnetic recording medium formed of a magnetic material with a large KU just before the application of write field. For the thermally-assisted magnetic recording technique, a method has been intensively developed, in which a near-field light generating element that includes a minute metal piece, so-called a plasmon antenna, is used for generating near-field light, and the magnetic recording medium is irradiated with the near-field light. For example, U.S. Pat. No. 6,768,556 B1 discloses a near-field light generating element that includes a metal scatterer with a strobilus shape formed on a substrate and a dielectric material film formed around the metal scatterer. And U.S. Pat. No. 6,649,894 B2 discloses a near-field light generating element made of a flat scatterer formed on the surface of a substrate.
However, a difficult problem may arise as described below in achieving thermally-assisted magnetic recording by using the above-described near-field light generating element.
In forming a near-field light generating element, an etching process is generally used for forming a plasmon antenna on a substrate. However, the etching process usually causes a substantially large step (depth difference) between the plasmon antenna and its surrounding. The amount of the step may reach, for example, several hundred nm (nanometers). After the etching process, the step and the plasmon antenna are covered with a dielectric material that is to form a waveguide, and the step may cause the formed waveguide to have an uneven surface or to have distortion within it. Whereas, in order to generate the sufficient amount of near-field light in the plasmon antenna, it is required to reduce the loss of light propagating through the waveguide as far as possible to properly irradiate the plasmon antenna with the light. Therefore, the uneven surface of the waveguide and the distortion within the waveguide has to be suppressed as far as possible. Moreover, when other head element part, for example, a main magnetic pole layer of a write head element is further formed over the waveguide, the unevenness and distortion of the layer also have to be avoided as far as possible in order to obtain desired characteristics. For this reason, the unevenness of the surface of the waveguide as an undercoat has to be suppressed.